Photomagnetic composition and printing process



Feb. 18, 1958 Y F. A. HAMM 2,823,999 PHOTOMAGNETIC CQMPOSITIQN AND PRINfrING PROCESS Filed Jan. 7, 1955 LIGHT-SEAG/T/VE RES/N WNTA/N/NG FERROMAGNE TIC IRON OXIDE Fi g1 l3 l2 l2, IMAGE m .2 W g 7/l/l/A Franklin/1.11am": INVENTOR.

ATTORNEYS United States Patent O cc PHOTOMAGNETIC COMPOSITION AND PRINTING PROCESS Franklin A. Hamm, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application January 7, 1955, Serial No. 480,487 8 Claims. (CI. 96-35) This invention relates tographic resist materials images therefrom.

The use of bichromated glue for preparing resists in the photoengraving industry is well known, and such materials have been used for many years. It is also well known that a pigmentpan be incorporated in the sensitized glue and a pigmented image thereby obtained. In the preparation of an image in this way, the coating of pigmented colloid must necessarily be quite thin so that exposure to light will harden the colloid throughout its entire thickness and the hardened portions will then adhere to the support upon washing with water. The unexposed portions will dissolve away and this process will yield a positive from a negative.

Reversal images may be obtained readily with gelatinosilver-halide sensitive layers, but such material is relatively expensive because of the content of silver salt and cannot be easily applied and processed. The application of sensitive material containing silver salts usually requires coating and drying apparatus and the material must be processed with photographic developers and fixing agents.

The process of my invention yields a positive image from a negative (or a negative from a positive). The material of my invention can be applied easily to most supports and can be processed in a simple manner. Its speed range is ideal for practical purposes, and it can be handled and coated in subdued daylight. Other advantages of my process and material will be evident from the following description of my invention.

The present invention makes use of polymer materials which are light-sensitive and which have properties superior to the mentioned bichromated materials. The polymeric materials used in my invention can be sensitized in a known manner to increase their sensitivity to actinic rays as much as a hundred times.

Accordingly, one object of my invention is to provide superior light-sensitive materials for making photographic resists which can be used as printing plates. Another object is to provide photographic resist materials which can be used for long periods of time without degradation of the printing surface. Still another object of my invention is to provide photographic resists which give a number of copies from the same printing surface, each of the copies being characterized by superior resolution and sharpness. Other objects will become apparent from a consideration of the following description and examples.

It is known that photographic resist materials can advantageously be prepared from synthetic resins which are sensitive to light upon prolonged exposure. Among the light-sensitive resins having this property are those obtained from monoethylenically-unsaturated compounds. Among the most useful of these synthetic polymers are those which contain a cinnamoyl group either in the form of an ester, or some other functional grouping, such as a chalcone. Such light-sensitive resins have been preto the preparation of phoand to methods of forming 2,823,999 Patented Feb. 18, 1958 viously described in a number of domestic and foreign patents, for example:

Allen et al., U. S. 2,566,302, issued Sept. 4, 1951 Minsk et al., U. S. 2,610,120, issued Sept. 9, 1952 Minsk et al., U. S. 2,670,285, issued Feb. 23, 1954 Minsk et al., U. S. 2,670,286, issued Feb. 23, 1954 Minsk et al., U. S. 2,670,287, issued Feb. 23, 1954 Minsk et al., U. S. 2,690,966, issued Oct. 5, 1954 Smith et al., U. S. 2,691,584, issued Oct. 12, 1954 Yates, Germany 807,894, ausgegeben July 9, 1951 The light-sensitive resins described in the above U. S. patents have a speed which is considerably higher than the customarily employed bichromated colloid. However, other light-sensitive resins which do not have sensitivity as high as that of the resins mentioned in the above U. S. patents can be employed in my invention, provided these resins have sensitivity which is at least equal to that of the bichromated gelatin mentioned above. The light-sensitive resins which have been found to be most useful in practicing my invention comprise those resins which contain the cinnamoyl group, which can be represented by the following formula:

Particularly useful light-sensitive resins comprise those obtained by esterifying polymers containing reactive hydroxyl groups with a cinnamoyl halide, such as cinnamoyl chloride. An example of such a resin is one obtained by esterifying polyvinyl alcohol with cinnamoyl chloride in accordance with the process described in the copending application of L. M. Minsk, U. S. Serial No. 207,052, filed January 20, 1951 (now U. S. Patent 2,725,372, issued November 29, 1955). Other light-sensitive resins which can be used in my invention are described in the copending applications of L. M. Minsk and W. P. Van Deusen, Serial Nos. 462,124 and 462,125, both filed October 13, 1954. Still another light-sensitive resin which can be employed in my invention is described in the copending application of L. M. Minsk, W. P. Van Deusen The resins described in the above prior art include light-sensitive polymers having recurring structural units having the formula:

wherein R represents a inonocyclic aryl group of the benzene series, such as phenyl, m-nitrophenyl, o-chlorophenyl, etc. groups. Other light-sensitive polymers having recurring structural units having the formula:

wherein R has the values given above, R is a hydrogen atom or a lower alkyl group (e. g., methyl, ethyl, propyl, butyl, etc.), and R is a monocyclic arylene group (e. g., phenylene, methylphenylene, etc.) can be employed (U. S. 2,566,302).

The instant invention takes advantage of the light-sew sitivity of the above-mentioned resins to form a relief image and also the magnetic properties of a ferromagnetic iron oxide, such as gamma ferric oxide (Fe O or ferroso-ferric oxide (Fe O Although a relief or resist image is formed in the light-sensitive resin, it is the magnetic property of the iron oxides which is the important aspect in the production of copies from the master. The quality of the master is not impaired by light, heat, moisture, and pressure. The magnetism is not readily inadvertently erased and the hardened resin has unusually good wear resistance.

In the accompanying drawing, the various figures show in enlarged cross-sectional view the structure of a repre sentative sensitive element of my invention at various stages in the process of producing printing plates having selected areas covered by polymeric resist images.

The manner of processing the photographic resist images of my invention can be outlined as follows: A solution in an organic solvent of a light-sensitive resin of the type described above, such as polyvinyl cinnamate, is uniformly mixed with a ferromagnetic iron oxide, such as gamma ferric oxide, and the mixture is coated uni formly on a surface. The coating is then exposed in the usual manner so that a relief image is formed after solvent development (see U. S. Patent 2,690,966). For example, exposure to a carbon arc for two minutes through a photographic positive or negative andsubsequent solvent development will produce a hard relief image consisting of the ferromagnetic iron oxide embedded in the hardened resin.

The relief image thus formed is magnetized or sensed using a recording head so that the relief image is now also a magnetic image. This magnetization can be accomplished in known manner, at various A. C. frequencies and speeds of motion of the magnetic matrix. However, the condition of 200 cycles/second, 8 volts, 21 milliamperes, and a speed of about 2.5 inches per second has proved to be very satisfactory. Contact recording (sensing) is desirable. Other methods of magnetizing the relief record can be employed. Such methods of magnetization are matters of common knowledge.

The magnetic latent image thus obtained is then developed to a magnetic visual image using finely divided iron (ferromagnetic). A suspension of this free iron (sometimes referred to as a magnetic ink) in carbon tetrachloride or other vehicle can be flooded over the relief image, or the master image can be immersed in the s uspension. In both cases, the magnetic lines of force in the magnetized relief image attract the soft iron (ferromagnetic) particles and hold them firmly in contact with the relief image. Regions in the master which are void of the hardened resin-ferromagnetic iron oxide matrix are free of developing iron. Also, the amount of iron attracted to regions in the relief image will be somewhat dependent on the thickness of the image at any given region.

Copies can best be made by contact transfer. One method of imbibition comprises using a moist, pressuresensitive adhesive transfer material, such as dye transfer paper. The dye transfer paper is slightly moistened on the gelatin side and this side is placed in contact with the developed master. Gentle pressure results in trans fer of the iron from the surface of the master matrix to the gelatin surface of the dye transfer paper. There is thus obtained an image on the transfer paper which consists of free iron embedded in gelatin. The record thus obtained can be preserved by spraying with a solution of an organic solvent containing dissolved resin, such as polymethyl methacrylate, polymethyl acrylate, etc.

Alternatively, transfer of the image from the resist material to a desired surface can be accomplished by placing the master image in contact with dry dye transfer paper with the gelatin coating thereof in contact with the developed master. When dry heat is applied to the rear surface of the dye transfer paper, transfer of the iron from the master surface occurs. A heat-sealing iron can also be used.

Copies can also be obtained from the relief image before it has been developed with the metallic iron 'by placing a thin sheet of paper, such as onion skin paper, in close contact with the magnetically sensed but undeveloped master. The magnetic reluctance of this thin copy paper is sufficiently low so that some magnetic lines of force pass through the paper and attract the finely divided free iron which has been cast on the outer surface of the thin paper. Thus, copies are made by flooding the air side of the sheet of paper, in contact with the relief image, with a suspension of the free iron. An unlimited number of copies can be made in this Way, and the images thus obtained can be made permanent by coating with a resinous solution as described above.

In general, transfer by means of paper having a gelatin coating or some other colloid coating thereon is preferred to the method using thin paper as described above, since the former method generally gives improved resolution. It is to be noted that in the method of my invention magnetic sensing is required only once. When the copy image becomes too weak, the master can be redeveloped with free iron as before. Six acceptable copies can be prepared, before redeveloping, using the dye transfer paper techniques described above.

My invention can be understood by consideration of the accompanying drawing and the following example which illustrates various means of employing the lightsensitive polymeric materials containing ferromagnetic iron oxides, and in particular, gamma ferric oxide. A lacquer containing 7.5 percent of polyvinyl cinnamate (U. S. 2,690,966) was ball-milled with gamma ferric oxide for a period of about 48 hours. The resulting mixture contained about 20 percent by weight of gamma ferric oxide. The resulting mixture which was in the form of a viscous solution or suspension was placed on a magnesium plate and whirled at a speed of approximately 5080 R. P. M., or if desired, by machine-coating methods, and the coating dried at room temperature, or elevated temperature in subdued light. After drying, the coating was about 15 microns thick. The coating was exposed to a line or halftone image for a minute to one and one-half minutes at one foot from a SS-ampere white flame arc, and after exposure, preferably in vacuum contact with the subject, was developed by washing in a tray or tank of a hydrocarbon, such as benzene, with gentle agitation for one-half to three minutes. After the solvent development, the resist image which had thus been formed was allowed to dry and was sensed magnetically by passing the relief image past a magnetic recording head which had been positioned in the chuck of a milling machine. The table speed was 2.5 inches per second and the length of the air gap in the recording head was 196 mils. The gap width was about 0.75 mil. The displacement normal to the motion of the milling machine table was indexed at mils so that an overlap of 46 mils occurred during each track length. In order to avoid white separation lines in the printed copies, it was found that the length of the magnetic recording head should be made approximately equal to the width of the area to be magnetized. Magnetic erasure is thus avoided.

The resist image which has thus been magnetically sensed was then treated with powdered iron (ferromagnetic) as described above. The developed image was then placed in contact with moistened dye transfer paper. The image thus obtained had a resolving power of about 5 lines per mm. This resolving power can be improved by using small-size iron developing powder, controlling the amount of developing iron that attaches itself to the magnetized master, or controlling the pressure applied to the copy during imbibition.

7 My invention will be further illustrated by reference to the accompanying drawing. Fig. 1 shows a support 10 of any suitable material, such as cellulose acetate, coated with a layer 11 containing light-sensitive resin, such as polyvinyl cinnamate, containing a ferromagnetic iron xide, such as gamma ferric oxide. In Fig. 2 the benzene series, and gamma ferric light-sensitive material shown in Fig. 1 has been exposed to light under an image having transparent portions 12 and opaque portions 13. After development of the exposed element shown in Fig. 2 by means of an organic solvent, there is obtained the resist Lnage shown in Fig. 3. The image consists of raised portions 14 containing gamma ferric oxide or other ferromagnetic material. This resist image can then be magnetized as described above and the magnetized surface treated with iron powder to produce a visible record of the subject. This visi ble record can then be transferred to another surface, such as the dye transfer paper as described in detail above.

The light-sensitive resins employed in my invention can contain chemical sensitizing compounds of the type described in a number of the above U. S. patents, these sensitizing compounds serving to increase materially the speed and sensitivity of the light-sensitive resins. Those light-sensitive resins which have been obtained by esterifying apolymer containing reactive hydroxyl groups with a cinnamoyl halide have been found to be particularly useful in my invention. These light-sensitive resins generally have at least 60 percent of the free hydroxyl groups esterified. Such light-sensitive resins can advantageously contain from 6099.4 mol. percent of cinnamate ester groups, the remaining units being alcohol units (e. g., vinyl alcohol units).

In the above example, the developing ferromagnetic iron which was used was carbonyl iron, type G, sold by the General Aniline and Film Corp. It was found to be about 98 percent pure iron and to have a weightaverage diameter of about 8 microns. It was spherical in form. The polyvinyl cinnamate used in the above example was sensitized with a chemical sensitizer as described in U. S. Patent 2,690,966.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. A photomechanical resist composition comprising a polymeric material of esters of polyvinyl alcohol containing at least 60 mol. percent of recurring structural units having the formula:

wherein R represents a monocyclic aryl group of the enzene series as a combined carrier and light-sensitive material, and a ferromagnetic iron oxide.

2. A photomechanical resist composition comprising the ester of polyvinyl alcohol set forth in claim 1 as a combined carrier and light-sensitive material, and gamma ferric oxide.

3. A photographic element comprising a support having thereon a layer comprising a partially esterified, lightsensitive ester of polyvinyl alcohol containing at least 60 mol. percent of recurring structural units having the fllowing formula:

oHzoH- dcoH=oHR H wherein R represents a monocyclic aryl group of the oxide. 4. A photographic element comprising a support hav- 6 ing thereon a layer comprising a partially esterified, lightsensitive cinnamic acid ester of a polymeric material containing free hydroxyl groups and gamma ferric oxide.

5. A photomagnetic printing process wherein a photographic element comprising a support having thereon a layer comprising a partially esterified, light-sensitive ester of polyvinyl alcohol containing at least 60 mol. percent of recurring structural units having the formula:

wherein R represents a monocyclic aryl group of the benzene series and ferromagnetic iron oxide is (1) exposed to an image, (2) the thus exposed photographic element is developed to a relief image by means of an organic solvent, (3) the relief image is sensed magnetically, (4) the magnetized relief image is developed with ferromagnetic iron in finely divided form, and (5) the finely divided ferromagnetic iron is transferred to a receiving sheet having coated thereon a gelatin layer.

6. A photomagnetic printing process as defined in claim 5 wherein the ferromagnetic iron oxide is gamma ferric oxide.

7. A photomagnetic printing process as defined in claim 6 wherein the partially esterified, light-sensitive ester of polyvinyl alcohol consists of from 60 to 99.4 mol. percent of recurring structural units having the formula:

-oHioH C CH=OH CdH5 I; the remaining recurring units being vinyl alcohol structural units.

References Cited in the file of this patent UNITED STATES PATENTS 494,526 Forster Mar. 28, 1893 2,500,052 Yackel Mar. 7, 1950 2,525,601 Howell Oct. 10, 1950 2,654,681 Lueck Oct. 6, 1953 2,690,966 Minsk et a1. Oct. 5, 1954 General Electric Review, July 1952, vol. 55, N0. 4 101/E1. Dig, pp 20, 21, 22 and 61. 

1. A PHOTOMECHANICAL RESIST COMPOSITION COMPRISING A POLYMERIC MATERIAL OF ESTERS OF POLYVINYL ALCOHOL CONTAINING AT LEAST 60 MOL. PERCENT OF RECURRING STRUCTURAL UNITS HAVING THE FORMULA: 